I raised the C issue with SC22 WG14, and the editor has agreed that the
next revision will change 7.19.6.2 para 16, 7.19.6.4 para 3, 7.19.6.7
para 3, and 7.19.6.9 para 3 from:
"The Xscanf function returns the value of the macro EOF if an input
failure occurs before any conversion."
to
"The Xscanf function returns the value of the macro EOF if an input
failure occurs before the first conversion (if any)."
Hope that helps!
On Fri, 2009-01-16 at 10:55 +0000, Geoff Clare wrote:
> @ page 934 line 31304 section fscanf objection [gwc fscanf return]
>
> Problem:
>
> Edition of Specification (Year): 2008
>
> Defect code : 1. Error
>
> In austin-group-l 11809, Vincent Lefèvre identified a conflict with
> the C Standard:
>
> ---- begin quote ----
>
> I think there is a contradiction between POSIX.1-2008 and the
> ISO C standard concerning fscanf when an input failure occurs
> after the first conversion.
>
> The ISO C standard (at least N1124 and N1336) says:
>
> 7.19.6.2 The fscanf function
>
> 4 The fscanf function executes each directive of the format in turn.
> If a directive fails, as detailed below, the function returns.
> Failures are described as input failures (due to the occurrence
> of an encoding error or the unavailability of input characters),
> or matching failures (due to inappropriate input).
>
> 16 The fscanf function returns the value of the macro EOF if an
> input failure occurs before any conversion. Otherwise, the
> function returns the number of input items assigned, which can
> be fewer than provided for, or even zero, in the event of an
> early matching failure.
>
> For instance, let us consider
>
> n = fscanf (stdin, "%d %d", &x, &y);
>
> where an input failure occurs *after* the first %d conversion (and
> before the second one). According to the C standard, n should be
> equal to 1 because
> * the input failure occurred *after* the first conversion,
> * 1 input item (exactly) has been assigned.
>
> However POSIX.1-2008 says (page 934):
>
> Upon successful completion, these functions shall return the number
> of successfully matched and assigned input items; this number can be
> zero in the event of an early matching failure. If the input ends
> before the first matching failure or conversion, EOF shall be returned.
> If any error occurs, EOF shall be returned, and errno shall be set to
> indicate the error. If a read error occurs, the error indicator for
> the stream shall be set.
>
> I wonder what POSIX really means by "If any error occurs, EOF shall be
> returned [...]". I suppose this means "input failure" in C (as opposed
> to "matching failure"). But, as shown above, the C standard does the
> difference between these two kinds of failure only when the failure
> occurs before the first conversion (indeed one gets EOF in case of an
> input failure, and 0 in case of a matching failure).
>
> ---- end quote ----
>
> An interpretation should be issued stating that POSIX defers to the
> C Standard here, and conforming implementations must behave as
> described in the C Standard. The POSIX text should be corrected in
> TC1 to remove the conflict.
>
> During discussions it emerged that, by a strict reading, the
> phrase "before any conversion" is ambiguous, although the intention
> is clear (at least, it is to native English speakers). It was
> proposed to use the phrase "before the first successful conversion"
> instead, but this has a couple of problems:
>
> 1. If the error occurs before the first conversion, then that
> conversion never happens and cannot be thought of as "successful".
>
> 2. Even if the word "successful" is removed, it is still not clear
> whether the error has to occur before reading the first byte of
> input that would be used in the conversion, or if the requirement
> also applies after at least one such byte has been read but with
> more bytes needed to finish the conversion.
>
> I propose to use "without any successful conversions having been
> made" instead.
>
> Action:
>
> Change
>
> "If the input ends before the first matching failure or conversion,
> EOF shall be returned. If any error occurs, EOF shall be returned,
> [CX]and errno shall be set to indicate the error[/CX]. If a read
> error occurs, the error indicator for the stream shall be set."
>
> to
>
> "If the input ends without any successful conversions having been
> made, and without a matching failure having occurred, EOF shall be
> returned. If an error occurs without any successful conversions
> having been made, and without a matching failure having occurred,
> EOF shall be returned [CX]and errno shall be set to indicate the
> error[/CX]. If a read error occurs, the error indicator for the
> stream shall be set."
>
> Make the same change to the fwscanf() page (P988 L33162).
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